1. Field of the Invention
The present invention relates to a power source device and, more particularly, to means for estimating the remaining electricity of a portable data modem powered by a battery, and the display of the efficient use of the battery.
2. Description of the Related Art
A power source device, which executes a power supply to a personal computer or similar electronic apparatus and informs the computer or apparatus of the consumption state of a battery, is described in, for example, Japanese Patent Laid-Open Application No. 36817/1992 (JP-A-04-36817). The power source device has a battery, a current sensor, a voltage sensor, and a capacity detector. The current sensor and voltage sensor measure the source current and source voltage of the battery, respectively. The capacity detector calculates a discharge energy by integrating the measured current and voltage by a time and estimates the remaining capacity of the battery.
The estimated remaining capacity is sent to the electric apparatus or computer to be supplied the power from the battery. In response, a controller installed in the electronic apparatus or computer makes the remaining capacity of the battery display.
In the conventional power source device described above, it is possible for a user to confirm the remaining capacity of the battery qualitatively. For instance, "60% remaining" is displayed. However, when it comes to the quantitative aspect, such a power source device cannot show specifically a period of time for which the battery is still usable, or how much capacity of a data signal can still be transmitted or received.
Moreover, in a data modem for a computer or similar device powered by one of a plurality of batteries, such as manganese battery or alkaline-manganese battery, each battery has a different discharge characteristic. Hence, the estimation of the remaining capacity involves noticeable errors and, therefore, do not withstand practical use.